Optical fibers are used as a signal transmitting means for transmitting signals inside communication devices or computers and to connect such devices to other devices or power sources. Because these optical fibers are very thin, the optical transmitting efficiency of the optical fibers deteriorates when they are sharply bent. For this reason, it is necessary to conduct wiring using optical fiber wiring boards on which the optical fibers are interposed between soft resin members.
Japanese Examined Patent Publication Nos. 2574611, 2735464 and 2807403 and Japanese Unexamined Patent Publication Nos. 7-248420 and 8-240732 disclose a technique in which optical fibers are laid on an adhesive layer which is provided on a film made of Kapton™ or Mylar™ so as to form a wiring pattern and then coating is conducted on it by the same material. However, since films having minimal flexibility cover both faces of the wiring board, the flexibility of the optical fiber wiring board is substantially impaired, and the working properties are deteriorated. Further, heat and pressure requirements during the coating process render it difficult to mass-produce the above optical fibers.
Japanese Unexamined Patent Publication Nos. 11-258447, 2000-19356, 2000-147266, 2000-206341 and 2000-231046 disclose an optical fiber wiring board having optical fibers laid on an adhesive layer so as to form a wiring pattern, Subsequently, the periphery of the wiring pattern is surrounded by a weir-shaped object and a protective resin layer is formed in the portion surrounded by the weir-shaped object by means of melting or coating. This type optical fiber wiring board is excellent in flexibility because only one film is used. However, it is complicated to form the weir-shaped object and the protective resin layer. For the above reasons, it is difficult to mass-produce this type optical fiber wiring board as well.
Japanese Unexamined Patent Publication No. 11-506546 discloses an optical fiber ribbon cable in which the optical fibers are interposed between adhesive tapes. This patent publication relates to an optical fiber ribbon cable that is used in a linear form so that the optical fibers can be easily connected and its' manufacturing method. This patent publication does not relate to a structure of optical fibers that can be easily bent.
FIG. 5 is a schematic illustration for explaining problems that occur in the prior art described above. FIG. 5(A) illustrates a state in which the optical fiber wiring board must be bent as shown by the broken line, however, the optical fiber board is bent as shown by the solid line and the optical fibers are sharply bent and thus wrinkles are created. FIG. 5(B) illustrates a state in which the optical fibers are not completely covered with resin. In this situation, the optical fibers are not stabilized. Accordingly, there is a possibility that the transmitting characteristic of the optical fibers will becomes unstable.
The present invention has been developed to solve the above problems. It is an object of the present invention to provide an optical fiber wiring board characterized in that the optical fiber wiring board can be easily manufactured and bent and further the optical fibers can be stably held on the optical fiber wiring board.